There are some principles in the design of Pynsist which have led me to turn
down potentially useful options. I’ve tried to explain them here so that I can
link to this rather than summarising them each time.

Pynsist is largely a simplifying wrapper around NSIS: it provides an easy way to do a subset of
the things NSIS can do. All simplifying wrappers come under pressure from
people who want to do something just outside what the wrapper currently
covers: they’d love to use the wrapper, if it just had one more option. But
if we keep adding options, eventually the simplifying wrapper becomes a
convoluted layer of extra complexity over the original system.

I’m very keen to keep installers as simple as possible. There are all
sorts of clever things we could do at install time. But it’s much harder to
write and test the NSIS install code than the Python build code, and errors
when the end user installs your software are a bigger problem than errors
when you build it, because you’re better able to understand and fix them.
So Pynsist does as much as possible at build time so that the installer can
be simple.

Pynsist has a limited scope: it builds Windows installers for Python
applications. Mostly GUI applications, but it does also have support for
adding command-line tools. I don’t plan to add support for other target
platforms or languages.

If you want to do something which Pynsist doesn’t support, there are several
ways it can still help you:

Generate an nsi script: You can run Pynsist once with the
--no-makensis option. In the build directory, you’ll find a file
installer.nsi, which is the script for your installer. You can modify
this and run makensisinstaller.nsi yourself to build the installer.

Write a custom template: Pynsist uses Jinja templates to create the
nsi script. You can write a custom template and specify it in the
Build section in your config file. Custom templates can inherit from
the templates in Pynsist and override blocks, so you have a lot of control
over the installer this way.

Cannibalise the code: Pull out whatever pieces are useful to you from
Pynsist and use them in your build scripts. There are the installer templates,
code to find and download wheels from PyPI, to download Python itself, to
create command-line entry points, to find makensis.exe on Windows, and so
on. You can take specific bits to reuse, or copy the whole thing and apply
some changes.